Polyamides

ABSTRACT

Polyamide whose main chain contains a chemically bound N-alkyllactam, and processes for preparing such a polyamide and fibers, films and moldings comprising such a polyamide.

This application claims priority from PCT/EP04/004816 filed May 6, 2004and German Application DE 103 21 789.4 filed May 14, 2003, thedisclosures of each application are incorporated herein by reference.

The present invention relates to a polyamide whose main chain contains achemically bound N-alkyllactam.

The present invention further relates to a process for preparing such apolyamide and also to fibers, films and moldings comprising at least onesuch polyamide.

Polyamides, especially nylon-6 and nylon-6,6, are industrially importantpolymers. They are typically prepared from suitable monomers, such ascaprolactam, adipic acid or hexamethylenediamine, which are reacted inthe presence of water.

Polyamide polymers are typically shaped into molding compositions, forexample into fibers, films or moldings.

Such molding compositions are often exposed to forces in use; theseforces can lead to rupture of the molding composition and hence todestruction of the molding composition.

The yardstick is the tensile strain at break ε_(b) or the nominal strainε_(t) as per DIN EN ISO 10350-1 in conjunction with DIN EN ISO 527-1.

The tensile strain at break indicates the relative elongation at thebreaking stress when the break takes place before the yield point isreached; the nominal strain indicates relative elongation beyond theyield point. Elongation is reversible up to the yield point andirreversible beyond the yield point.

A high tensile strain at break is a desirable property for a moldingcomposition, since it means that the molding composition is capable ofabsorbing an applied force elastically, returning back to the originalshape after the force has died down.

It is an object of the present invention to provide a polyamide whichhas an enhanced DIN EN ISO 527-1 tensile strain at break compared withprior art polyamides and also a process for preparing such a polyamide.

We have found that this object is achieved by the polyamide defined atthe beginning, a process for preparing it and also fibers, films andmoldings comprising at least one such polyamide.

Polyamides are herein to be understood as being homopolymers,copolymers, blends and grafts of synthetic long-chain polyamides havingrecurring amide groups in the polymer main chain as an essentialconstituent. Examples of such polyamides are nylon-6 (polycaprolactam),nylon-6,6 (polyhexamethyleneadipamide), nylon-4,6(polytetramethyleneadipamide), nylon-6,10 (polyhexamethylenesebacamide),nylon-7 (polyenantholactam), nylon-11 (polyundecanolactam ), nylon-12(polydodecanolactam). As well as polyamides known by the generic name ofnylon, polyamides further include the aramids (aromatic polyamides),such as poly-meta-phenyleneisophthalamide (NOMEX® fiber, U.S. Pat. No.3,287,324) or poly-para-phenyleneterephthalamide (KEVLAR® fiber, U.S.Pat. No. 3,671,542).

Polyamides can in principle be prepared by two methods.

In a polymerization from dicarboxylic acids and diamines and also in apolymerization from amino acids or their derivatives, such asaminocarbonitriles, aminocarboxamides, aminocarboxylate esters oraminocarboxylate salts, the amino and carboxyl end groups of thestarting monomers or starting oligomers react with one another to forman amide group and water. The water can subsequently be removed from thepolymer. In a polymerization from aminocarboxamides, the amino and amideend groups of the starting monomers or starting oligomers react with oneanother to form an amide group and ammonia. The ammonia can subsequentlybe removed from the polymer. When amino-carboxylic esters arepolymerized, the amino and ester end groups of the starting monomers oroligomers react with one another to form an amide group and alcohol. Thealcohol can subsequently be removed from the polymer. In thepolymerization of amino-carboxylic nitriles, the nitrile groups canfirst react with water to form amide or carboxyl groups and theresulting aminocarboxylic amides or acids can be reacted as described.This polymerization reaction is customarily known as a polycondensation.

A polymerization from lactams as starting monomers or starting oligomersis customarily known as a polyaddition.

Such polyamides are obtainable by conventional processes, as describedfor example in DE-A-14 95 198, DE-A-25 58 480, EP-A-129 196 or in:Polymerization Processes, Interscience, New York, 1977, pages 424-467,especially pages 444-446, from monomers selected from the groupconsisting of lactams, omega-aminocarboxylic acids,omega-aminocarbonitriles, omega-aminocarboxamides,omega-aminocarboxylate salts, omega-aminocarboxylate esters, equimolarmixtures of diamines and dicarboxylic acids, dicarboxylic acid/diaminesalts, dinitriles and diamines or mixtures thereof.

Useful monomers include

monomers or oligomers of a C₂ to C₂₀, preferably C₂ to C₁₈,arylaliphatic or, preferably, aliphatic lactam such as enantholactam,undecanolactam, dodecanolactam or caprolactam,

monomers or oligomers of C₂ to C₂₀, preferably C₃ to C₁₈,aminocarboxylic acids such as 6-aminocaproic acid or 11-aminoundecanoicacid, and salts thereof such as alkali metal salts, for example lithium,sodium or potassium salts,

monomers or oligomers of C₂ to C₂₀, preferably C₃ to C₁₈,aminocarbonitriles such as 6-aminocapronitrile or11-aminoundecanonitrile,

monomers or oligomers of C₂ to C₂₀ amino acid amides such as6-aminocapronamide or 11-aminoundecanamide,

esters, preferably C₁-C₄ alkyl esters, such as methyl, ethyl, n-propyl,i-propyl, n-butyl, i-butyl or s-butyl esters, of C₂ to C₂₀, preferablyC₃ to C₁₈, aminocarboxylic acids, such as 6-aminocaproic acid esters,for example methyl 6-aminocaproate, or 11-aminoundecanoic acid esters,for example methyl 11-aminoundecanoate,

monomers or oligomers of a C₂ to C₂₀, preferably C₂ to C₁₂,alkyldiamine, such as tetramethylenediamine or, preferably,hexamethylenediamine,

with a C₂ to C₂₀, preferably C₂ to C₁₄, aliphatic dicarboxylic acid ormono- or dinitriles thereof, such as sebacic acid, dodecanedioic acid,adipic acid, sebacic acid dinitrile, decane-1,10-dinitrile oradiponitrile,

monomers or oligomers of a C₂ to C₂₀, preferably C₂ to C₁₂,alkyldiamine, such as tetramethylenediamine or, preferably,hexamethylenediamine,

with a C₈ to C₂₀, preferably C₈ to C12, aromatic dicarboxylic acid orderivatives thereof, for example chlorides, such asnaphthalene-2,6-dicarboxylic acid, preferably isophthalic acid orterephthalic acid,

monomers or oligomers of a C₂ to C₂₀, preferably C₂ to C₁₂,alkyldiamine, such as tetramethylenediamine or, preferably,hexamethylenediamine,

with a C₉ to C₂₀, preferably C₉ to C₁₈, arylaliphatic dicarboxylic acidor derivatives thereof, for example chlorides, such as o-, m- orp-phenylenediacetic acid,

monomers or oligomers of a C₆ to C₂₀, preferably C₆ to C₁₀, aromaticdiamine, such as m- or p-phenylenediamine,

with a C₂ to C₂₀, preferably C₂ to C₁₄, aliphatic dicarboxylic acid ormono- or dinitriles thereof, such as sebacic acid, dodecanedioic acid,adipic acid, sebacic acid dinitrile, decane-1,10-dinitrile oradiponitrile,

monomers or oligomers of a C₆ to C₂₀, preferably C₆ to C₁₀, aromaticdiamine, such as m- or p-phenylenediamine,

with a C₈ to C₂₀, preferably C₈ to C₁₂, aromatic dicarboxylic acid orderivatives thereof, for example chlorides, such asnaphthalene-2,6-dicarboxylic acid, preferably isophthalic acid orterephthalic acid,

monomers or oligomers of a C₆ to C₂₀, preferably C₆ to C₁₀, aromaticdiamine, such as m- or p-phenylenediamine,

with a C₉ to C₂₀, preferably C₉ to C₁₈, arylaliphatic dicarboxylic acidor derivatives thereof, for example chlorides, such as o-, m- orp-phenylenediacetic acid,

monomers or oligomers of a C₇ to C₂₀, preferably C₈ to C₁₈,arylaliphatic diamine, such as m- or p-xylylenediamine,

with a C₂ to C₂₀, preferably C₂ to C₁₄, aliphatic dicarboxylic acid ormono- or dinitriles thereof, such as sebacic acid, dodecanedioic acid,adipic acid, sebacic acid dinitrile, decane-1,10-dinitrile oradiponitrile,

monomers or oligomers of a C₇ to C₂₀, preferably C₈ to C₁₈,arylaliphatic diamine, such as m- or p-xylylenediamine,

with a C₆ to C₂₀, preferably C₆ to C₁₀, aromatic dicarboxylic acid orderivatives thereof, for example chlorides, such asnaphthalene-2,6-dicarboxylic acid, preferably isophthalic acid orterephthalic acid,

monomers or oligomers of a C₇ to C₂₀, preferably C₈ to C₁₈,arylaliphatic diamine, such as m- or p-xylylenediamine,

with a C₉ to C₂₀, preferably C₉ to C₁₈, arylaliphatic dicarboxylic acidor derivatives thereof, for example chlorides, such as o-, m- orp-phenylenediacetic acid,

and homopolymers, copolymers, blends and grafts of such startingmonomers or starting oligomers.

Useful oligomers include, in particular, the dimers, trimers, tetramers,pentamers or hexamers of said monomers or of mixtures of such monomers.

In a preferred embodiment, the lactam used is caprolactam, the diamineused is tetramethylenediamine, hexamethylenediamine or their mixturesand the dicarboxylic acid used is adipic acid, sebacic acid,dodecanedioic acid, terephthalic acid, isophthalic acid or mixturesthereof. Particular preference is given to the lactam being caprolactam,the diamine being hexamethylenediamine and the dicarboxylic acid beingadipic acid or terephthalic acid or their mixtures.

Particular preference is given to those starting monomers or startingoligomers which on polymerization lead to the polyamides nylon-6,nylon-6,6, nylon-4,6, nylon-6,10, nylon-6,12, nylon-7, nylon-11 ornylon-12 or the aramids poly-meta-phenylene-isophthalamide orpoly-para-phenyleneterephthalamide, especially to nylon-6 or nylon-6,6.

In a preferred embodiment, the polyamides may be prepared using one ormore chain regulators. Useful chain regulators advantageously includecompounds having one or more, such as two, three or four, preferably twoin the case of systems in the form of fibers, amino groups reactive inpolyamide formation or one or more, such as two, three or four,preferably two in the case of systems in the form of fibers, carboxylgroups reactive in polyamide formation.

The first case provides polyamides wherein the monomers and chainregulators used for preparing said polyamide have a higher number ofamino groups, or their equivalents, used for forming said polymer chainthan carboxylic acid groups, or their equivalents, used for forming saidpolymer chain.

The second case provides polyamides wherein the monomers and chainregulators used for preparing said polyamide have a higher number ofcarboxylic acid groups, or their equivalents, used for forming saidpolymer chain than amino groups, or their equivalents, used for formingsaid polymer chain.

Useful chain regulators advantageously include monocarboxylic acids,such as alkane-carboxylic acids, for example acetic acid, propionicacid, such as benzene- or naphthalene-monocarboxylic acid, for examplebenzoic acid, dicarboxylic acids, such as C₄-C₁₀-alkanedicarboxylicacid, for example adipic acid, azelaic acid, sebacic acid, dodecanedioicacid, C₅-C₈-cycloalkanedicarboxylic acids, for examplecyclohexane-1,4-dicarboxylic acid, benzene- or naphthalenedicarboxylicacid, for example terephthalic acid, isophthalic acid,naphthalene-2,6-dicarboxylic acid, C₂ to C₂₀, preferably C₂ to C₁₂,alkylamines, such as cyclohexylamine, C₆ to C₂₀, preferably C6 to C₁₀,aromatic mono-amines, such as aniline, or C₇ to C₂₀, preferably C₈ toC₁₈, arylaliphatic monoamines, such as benzylamine, diamines, such asC₄-C₁₀-alkanediamines, for example hexamethylenediamine.

The chain regulators may be unsubstituted or substituted, for example byaliphatic groups, preferably C₁-C₈-alkyl groups, such as methyl, ethyl,i-propyl, n-propyl, n-butyl, i-butyl, s-butyl, n-pentyl, n-hexyl,n-heptyl, n-octyl, 2-ethylhexyl, OH, ═O, C₁-C₈-alkoxy, COOH,C₂-C₆-carbalkoxy, C₁-C₁₀-acyloxy, or C₁-C₁₆-alkylamino, sulfonic acid orsalts thereof, such as alkali or alkaline earth metal salts, cyano orhalogens, such as fluorine, chlorine, bromine. Examples of substitutedchain regulators are sulfoisophthalic acid and alkali or alkaline earthmetal salts thereof, such as lithium, sodium or potassium salts,sulfoisophthalic esters, for example with C₁-C₁₆-alkanols, orsulfoisophthalic acid mono- or diamides, especially with monomerssuitable for forming polyamides and bearing at least one amino group,such as hexamethylenediamine or 6-aminocaproic acid.

Preferred chain regulators are sterically hindered piperidinederivatives of the formula

where

-   R¹ is a functional group capable of amide formation with the polymer    chain of the polyamide,    -   preferably a group —(NH)R⁵, in which R⁵ is hydrogen or C₁-C₈        alkyl or a carboxyl group, or a carboxyl derivative, or a group        —(CH₂)_(x)(NH)R⁵, in which x is 1 to 6 and R⁵ is hydrogen or        C₁-C₈ alkyl, or a group —(CH₂)_(y)COOH, in which y is 1 to 6, or        a —(CH₂)_(y)COOH acid derivative, in which y is 1 to 6,    -   especially a group —NH₂,-   R² is an alkyl group, preferably a C₁-C₄ alkyl group such as methyl,    ethyl, n-propyl, i-propyl, n-butyl, i-butyl, s-butyl, t-butyl,    -   especially a methyl group,-   R³ is hydrogen, C₁-C₄ alkyl or O—R⁴, in which R⁴ is hydrogen or    C₁-C₇ alkyl,    -   R³ being hydrogen in particular.

In such compounds, steric hindrance usually prevents the tertiary aminogroups, and especially the secondary amino groups, of the piperidinering systems from reacting.

A particularly preferred sterically hindered piperidine derivative is4-amino-2,2,6,6-tetramethylpiperidine.

A chain regulator may advantageously be used in amounts of not less than0.001 mol %, preferably not less than 0.01 mol %, especially not lessthan 0.03 mol % and more preferably not less than 0.08 mol %, based on 1mol of acid amide groups of the polyamide.

A chain regulator may advantageously be used in amounts of not more than2.0 mol %, preferably not more than 1 mol %, especially not more than0.6 mol %, and more preferably not more than 0.5 mol %, based on 1 molof acid amide groups of the polyamide.

In accordance with the present invention, the main chain of thepolyamide contains a chemically bound N-alkyllactam.

Whenever the present invention refers to N-alkyllactam, the term shallcomprehend not only such an N-alkyllactam but also a mixture of suchN-alkyllactams.

In a preferred embodiment, the N-alkyllactam is an N—C₁-C₁₀-alkyllactam,preferably an N-alkyllactam selected from the group consisting ofN-methyllactam, N-ethyllactam, N-n-propyllactam, N-i-propyllactam,N-n-butyllactam, N-i-butyllactam and N-t-butyllactam, especially anN-ethyllactam.

Useful N-alkyllactams are also those having from 3 to 10 carbon atoms inthe lactam ring, preferably those in which the lactam ring is selectedfrom the group consisting of pyrrolidone, piperidone and caprolactam,especially caprolactam.

The lactam ring may be substituted, for example by one or more alkylgroups, preferably C₁-C₁₀-alkyl groups, especially methyl, ethyl,n-propyl, i-propyl, n-butyl, i-butyl, t-butyl, halogen, such asfluorine, chlorine, bromine, haloalkyl, such as trifluoromethyl. In apreferred embodiment, the lactam ring is unsubstituted.

In a particularly preferred embodiment, the N-alkyllactam isN-ethylcaprolactam.

Such N-alkyllactams and their preparation are known per se.

The level of N-alkyllactam may advantageously be not more than 0.001 mol%, preferably not less than 0.01 mol %, especially not more than 0.03mol % and more preferably not less than 0.08 mol %, based on 1 mol ofacid amide groups of the polyamide.

The level of N-alkyllactam may advantageously be not more than 2.0 mol%, preferably not more than 1 mol %, especially not more than 0.6 mol %and more preferably not more than 0.5 mol %, based on 1 mol of acidamide groups of the polyamide.

The polyamides of the present invention are obtainable in a processwhich comprises converting monomers, oligomers or mixtures thereofsuitable for forming a polyamide into a polyamide in the presence of anN-alkyllactam or of a compound from which an N-alkyllactam is releasedunder the reaction conditions for preparing the polyamide.

The polyamides of the present invention may be prepared using theprocess conditions customary for preparing polyamides from thecorresponding monomers, as described for example in DE-A-14 95 198,DE-A-25 58 480, EP-A-129 196, DE-A-19 709 390, DE-A-35 34 817, WO99/38908, WO 99/43734, WO 99/43732, WO 00/24808, WO 01/56984 or inPolymerization Processes, Interscience, New York, 1977, pages 424-467,especially pages 444-446.

In a preferred embodiment, the polymerization or polycondensation of theprocess according to the present invention may be carried out in thepresence of at least one pigment. Preferred pigments are titaniumdioxide, preferably in the anatase or rutile crystal form, or coloredcompounds of the organic or inorganic kind. The pigments are preferablyadded in an amount from 0 to 5 parts by weight and especially from 0.02to 2 parts by weight, based in each case on 100 parts by weight ofpolyamide. The pigments may be added to the reactor with the startingmaterials or separately therefrom.

Furthermore, the polyamides may be prepared not only by the two,preferred processes mentioned but also by anionic polymerization.

An anionic polymerization process typically comprises reacting

-   a) a lactam or a mixture of lactams,-   b) a lactamate or a compound which releases a lactamate from a    lactam as per a), or mixtures of such components, and-   c) a polymerization-regulating activator    -   with one another to obtain a polyamide.

Processes for anionic polymerization of lactams, also known as alkalinepolymerization of lactams, and also suitable compounds a), b) and c) aregeneral common knowledge, for example from U.S. Pat. No. 3,206,418, U.S.Pat. No. 3,207,713, U.S. Pat. No. 3,494,999, U.S. Pat. No. 3,793,255,U.S. Pat. No. 4,233,433, U.S. Pat. No. 4,393,193, U.S. Pat. No.4,503,014, U.S. Pat. No. 5,747,634, WO-A-00/58387, WO-A-01/49906,International Polymer Processing 16(2) (2001) 172-182 or Fourné,Synthetische Fasern, Carl Hanser Verlag, Munich/Vienna, 1995, pages38-39.

The polyamides of the present invention may advantageously be used forproducing fibers, films and moldings comprising such a polyamide or,more specifically, consisting of such a polyamide.

EXAMPLES

The solution viscosity reported in the examples was measured as arelative solution viscosity in 96% sulfuric acid as per DIN 51562-1 to-4.

Specifically, 1 g of polymer was weighed out per 100 ml of solution andthe flow time was measured in a Ubbelohde viscometer against the puresolvent.

Inventive Example 1

In a pressure vessel, 500 kg (4419 mol) of caprolactam, 50 kg ofcompletely ion-free water and 1 271 g (9 mol) of N-ethylcaprolactam wereheated under nitrogen to an internal temperature of 270° C., immediatelythereafter let down to atmospheric over an hour, supplementarilycondensed for 60 minutes and discharged.

The discharged polyamide was extracted, dried and heat-treated in thesolid state to a relative solution viscosity of RV=2.72.

Comparative Example 1

Inventive example 1 was repeated except that no N-ethylcaprolactam wasadded. The relative solution viscosity after heat treatment was RV=2.73.

Example 2

The polymers prepared as per inventive example 1 and comparative example1 were compounded in an extruder with 30% by weight of OCF 123 D 10 Pglass fiber (from OCF) and 7% by weight of Lupolen KR 1270 rubber (fromBASF Aktiengesellschaft) (the percentages are based on theready-compounded material). The relative solution viscosity aftercompounding was 2.80 in both cases.

The two compounded materials were subjected to a measurement of thetensile strain at break as per ISO 527. The following result wasobtained:

Normalized tensile strain at break for polymer from inventive example1:6% Normalized tensile strain at break for polymer from comparativeexample 1:4%

Thus, the polymer prepared as per inventive example 1 has a 50% highertensile strain at break than the polymer prepared as per comparativeexample 1.

1. A polyamide whose main chain comprises a chemically boundN-alkylcaprolactam wherein the N-alkylcaprolactam content is in therange from 0.001 mol % to 2 mol %, based on 1 mol of acid amide groupsof the polyamide.
 2. The polyamide according to claim 1 wherein theN-alkylcaprolactam is an N—C₁-C₁₀-alkylcaprolactam.
 3. The polyamideaccording to claim 1 wherein the N-alkylcaprolactam is selected from thegroup consisting of N-n-methylcaprolactam, N-i-ethylcaprolactam,N-n-propylcaprolactam, N-i-propylcaprolactam, N-n-butylcaprolactam,N-i-butylcaprolactam and N-t-butylcaprolactam.
 4. The polyamideaccording to claim 1 wherein the N-alkylcaprolactam is anN-ethylcaprolactam.
 5. A process for preparing a polyamide, whichcomprises converting monomers suitable for forming a polyamide in thepresence of an N-alkylcaprolactam according to claim
 2. 6. A process forpreparing a polyamide, which comprises converting oligomers suitable forforming a polyamide into a polyamide in the presence of anN-alkylcaprolactam according to claim
 2. 7. Fibers, films and moldingscomprising a polyamide according to claim
 1. 8. The polyamide accordingto claim 3 wherein the N-alkylcaprolactam content is in the range from0.001 mol % to 2 mol %, based on 1 mol of acid amide groups of thepolyamide.
 9. The polyamide according to claim 4 wherein theN-alkylcaprolactam content is in the range from 0.001 mol % to 2 mol %,based on 1 mol of acid amide groups of the polyamide.